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Old 28th February 2013, 03:53 AM   #1
impsick is offline impsick  United States
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Default Suggestions on regulating -70v

Trying to make a power supply for a mic that requires +70v -70v. I found the TL783 for regulating +70v but haven't found anything to regulate the -70v.

Any suggestions, tricks, schematics, tips would be awesome. thanks
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Old 28th February 2013, 05:05 AM   #2
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For such low currents that may happen in mic & preamps, a zener diode
is sufficient, for both the rails. You might want the zeners and the resistors
to be 1/2 W. Add two more decoupling capacitors and you've got a six components voltage regulator for + and - 70 V.
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Old 28th February 2013, 01:53 PM   #3
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My suppliers don't stock 70 volt zener diodes but they do stock the NZX36, 1N5258, and 1N4753, all of which are 36 volt zeners. So you could build zener regulated, capacitance multipled supplies using MJE340 / MJE350 as series pass regulators. 6 components per rail.
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Old 28th February 2013, 08:25 PM   #4
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awesome, thanks for the input guys!
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Old 28th February 2013, 09:09 PM   #5
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if you have two secondaries, you can use a positive chip regulator "upside down" as it were, to regulate the voltage between the ground and the negative. you must form the ground point after both regs, not before

also, you can use a lower voltage regulator and attach zeners to the adjust to take it up, so long as the drop between Vin and Vout doesn't exceed spec, and you don't short the output by accident
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Old 1st March 2013, 01:55 AM   #6
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Quote:
Originally Posted by Robert Kesh View Post
if you have two secondaries, you can use a positive chip regulator "upside down" as it were, to regulate the voltage between the ground and the negative. you must form the ground point after both regs, not before

also, you can use a lower voltage regulator and attach zeners to the adjust to take it up, so long as the drop between Vin and Vout doesn't exceed spec, and you don't short the output by accident
do you have an example schematic for your first suggestion?
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Old 1st March 2013, 02:15 AM   #7
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If you're using a 3-terminal regulator, just using a sufficiently large resistor on the Adj pin could work. Take a look at the application notes; there's a wealth of information there on power supply design.

Alternatively, this might be a case where shunt regulation makes sense. I have a hunch that could be electrically quieter than using a zener. I assume that a microphone needs very quiet supply rails.
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Old 1st March 2013, 09:27 AM   #8
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Quote:
Originally Posted by impsick View Post
do you have an example schematic for your first suggestion?
Click the image to open in full size.

protection diodes, caps, resistor values, should all be as datasheet
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Old 1st March 2013, 09:29 AM   #9
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Quote:
Originally Posted by dangus View Post
If you're using a 3-terminal regulator, just using a sufficiently large resistor on the Adj pin could work. Take a look at the application notes; there's a wealth of information there on power supply design.

Alternatively, this might be a case where shunt regulation makes sense. I have a hunch that could be electrically quieter than using a zener. I assume that a microphone needs very quiet supply rails.
I have always wonderd about the PSRR of a mic, and can never find any info. Luckily the standard 48V phantom power is easily regulated with a LM317HV
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Old 3rd March 2013, 09:39 PM   #10
impsick is offline impsick  United States
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Thanks for that schematic Robert. That totally helps.
this might be a stupid question but say I also wanted 5v. Can i add another LM7805 to one of the windings or would I need another winding to do that with this set up? Thanks
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